DESCRIPTION: The long term goal of this proposal is to prove that de novo DNA methylation results in the inactivation of expression of tumor suppressor genes and is a critical event in carcinogenesis. The specific hypothesis is that a critical event in Ni-induced transformation involves an initial site-specific increase in chromatin condensation at borders of heterochromatin, triggering de novo DNA methylation, yielding loss of expression of neighboring tumor suppressor genes. By inducing de novo methylation, Ni may reprogram gene expression of critical tumor suppressor genes for subsequent cell generations, thus triggering carcinogenesis. To address this hypothesis, this investigator will explore Ni-induced effects in accordance with the following specific aims: (1) To investigate whether carcinogenic Ni compounds in intact cells and addition of Ni to isolated nuclei induce site-specific chromatin condensation and DNA methylation that leads to loss of target gene transcription in a transgenic Ni responsive and nonresponsive model system. (2) To investigate whether other mutagenic and non-mutagenic carcinogens trigger similar site-specific chromatin condensation and DNA methylation changes in the target gene of Ni responsive and nonresponsive model systems. (3) To investigate the molecular mechanisms by which the expression of the Rb gene and cdk4 kinase inhibitor p16 are inactivated during Ni-induced transformation of human osteosarcoma cells from anchorage-dependent to anchorage-independent growth. (4) To investigate the consequence of inhibiting and activating DNA methylation on HOS cell transformation alone or the transformed state as induced by Ni, as well as other carcinogens.